The present invention relates to shock absorbers suitably used to damp vibrations of automobiles, for example.
In vehicles such as two- or four-wheeled automobiles, a hydraulic shock absorber is generally provided between a wheel-side member and a vehicle body-side member to damp vertical vibrations, etc. generated during running of the vehicle. This hydraulic shock absorber uses an actuator to change the orifice area through which a hydraulic fluid passes, thereby enabling damping force generated to be properly adjusted over a range of from low damping force to high damping force. Moreover, the hydraulic shock absorber is additionally provided with a frequency-dependent mechanism (i.e. a mechanism whereby damping force reduces according to the input vibration frequency). The combination of the frequency-dependent mechanism and the damping force control mechanism allows an improvement in the vehicle ride quality (for example, see Japanese Patent Application Publication No. Hei 06-94065).
The frequency-dependent mechanism makes it possible to provide reduced damping force for high-frequency vibration input even when damping force characteristics are set to “hard” as shown, for example, in FIG. 2 of Japanese Patent Application Publication No. Hei 06-94065.